Natural variation at the FRD3 MATE transporter locus reveals cross-talk between Fe homeostasis and Zn tolerance in Arabidopsis thaliana.

Zinc (Zn) is essential for the optimal growth of plants but is toxic if present in excess, so Zn homeostasis needs to be finely tuned. Understanding Zn homeostasis mechanisms in plants will help in the development of innovative approaches for the phytoremediation of Zn-contaminated sites. In this study, Zn tolerance quantitative trait loci (QTL) were identified by analyzing differences in the Bay-0 and Shahdara accessions of Arabidopsis thaliana. Fine-scale mapping showed that a variant of the Fe homeostasis-related FERRIC REDUCTASE DEFECTIVE3 (FRD3) gene, which encodes a multidrug and toxin efflux (MATE) transporter, is responsible for reduced Zn tolerance in A. thaliana. Allelic variation in FRD3 revealed which amino acids are necessary for FRD3 function. In addition, the results of allele-specific expression assays in F1 individuals provide evidence for the existence of at least one putative metal-responsive cis-regulatory element. Our results suggest that FRD3 works as a multimer and is involved in loading Zn into xylem. Cross-homeostasis between Fe and Zn therefore appears to be important for Zn tolerance in A. thaliana with FRD3 acting as an essential regulator.

Loss-of-function mutations in FGFR1 cause autosomal dominant Kallmann syndrome.

We took advantage of overlapping interstitial deletions at chromosome 8p11-p12 in two individuals with contiguous gene syndromes and defined an interval of roughly 540 kb associated with a dominant form of Kallmann syndrome, KAL2. We establish here that loss-of-function mutations in FGFR1 underlie KAL2 whereas a gain-of-function mutation in FGFR1 has been shown to cause a form of craniosynostosis. Moreover, we suggest that the KAL1 gene product, the extracellular matrix protein anosmin-1, is involved in FGF signaling and propose that the gender difference in anosmin-1 dosage (because KAL1 partially escapes X inactivation) explains the higher prevalence of the disease in males.

Presenting features and molecular genetics of primary hyperparathyroidism in the paediatric population.

AIM: To describe the presenting features and molecular genetics of primary hyperparathyroidism (PHPT) in the paediatric population. METHODS: Retrospective study of 63 children diagnosed with primary PHPT from 1998 to 2018. RESULTS: Compared to older children, infants were often asymptomatic (54% vs 15%, P = 0.002) with a milder form of PHPT. When symptomatic, children and adolescents mostly presented with non-specific complaints such as asthenia, depression, weight loss, vomiting or abdominal pain. A genetic cause of PHPT was identified in about half of this cohort (52%). The infancy period was almost exclusively associated with mutation in genes involved in the calcium-sensing receptor (CaSR) signalling pathway (i.e. CaSR and AP2S1 genes, 'CaSR group'; 94% of infants with mutations) whereas childhood and adolescence were associated with mutation in genes involved in parathyroid cell proliferation (i.e. MEN1, CDC73, CDKN1B and RET genes, 'cell proliferation group'; 69% of children and adolescents with mutations). Although serum calcium levels did not differ between the two groups (P = 0.785), serum PTH levels and the urinary calcium/creatinine ratio were significantly higher in 'cell proliferation group' patients compared to those in the 'CaSR group' (P = 0.001 and 0.028, respectively). CONCLUSION: Although far less common than in adults, PHPT can develop in children and is associated with significant morbidity. Consequently, this diagnosis should be considered in children with non-specific complaints and lead to monitoring of mineral homeostasis parameters. A genetic cause of PHPT can be identified in about half of these patients.

The cyclization of the 3,6-anhydro-galactose ring of iota-carrageenan is catalyzed by two D-galactose-2,6-sulfurylases in the red alga Chondrus crispus.

Carrageenans are sulfated galactans found in the cell walls of numerous red seaweeds (Rhodophyta). They are classified according to the number and the position of sulfate ester groups and the occurrence of 3,6-anhydro-galactose. Although the carrageenan biosynthesis pathway is not fully understood, it is usually accepted that the last step consists of the formation of a 3,6-anhydro ring found in kappa- and iota-carrageenans through the enzymatic conversion of d-galactose-6-sulfate or d-galactose-2,6-disulfate occurring in mu- and nu-carrageenan, respectively. We purified two enzymes, sulfurylase I (65 kD) and sulfurylase II (32 kD), that are able to catalyze the conversion of nu- into iota-carrageenan. We compared their sulfate release rates (i.e. arising from the formation of the anhydro ring) with the viscosity of the solution and demonstrated two distinct modes of action. In addition, we found that some mixtures of sulfurylase I and II lead to the formation of carrageenan solutions with unexpectedly low viscosities. We discuss the implication of these findings for the assembly of a densely aggregated matrix in red algal cell walls.

Impact of chloroplastic- and extracellular-sourced ROS on high light-responsive gene expression in Arabidopsis.

The expression of 28 high light (HL)-responsive genes of Arabidopsis was analysed in response to environmental and physiological factors known to influence the expression of the HL-responsive gene, ASCORBATE PEROXIDASE2 (APX2). Most (81%) of the HL-responsive genes, including APX2, required photosynthetic electron transport for their expression, and were responsive to abscisic acid (ABA; 68%), strengthening the impression that these two signals are crucial in the expression of HL-responsive genes. Further, from the use of mutants altered in reactive oxygen species (ROS) metabolism, it was shown that 61% of these genes, including APX2, may be responsive to chloroplast-sourced ROS. In contrast, apoplastic/plasma membrane-sourced H2O2, in part directed by the respiratory burst NADPH oxidases AtrbohD and AtrbohF, was shown to be important only for APX2 expression. APX2 expression in leaves is limited to bundle sheath parenchyma; however, for the other genes in this study, information on their tissue specificity of expression is sparse. An analysis of expression in petioles, enriched for bundle sheath tissue compared with distal leaf blade, in HL and control leaves showed that 25% of them had >10-fold higher expression in the petiole than in the leaf blade. However, this did not mean that these petiole expression genes followed a pattern of regulation observed for APX2.

A putative novel role for plant defensins: a defensin from the zinc hyper-accumulating plant, Arabidopsis halleri, confers zinc tolerance.

The metal tolerance of metal hyper-accumulating plants is a poorly understood mechanism. In order to unravel the molecular basis of zinc (Zn) tolerance in the Zn hyper-accumulating plant Arabidopsis halleri ssp. halleri, we carried out a functional screening of an A. halleri cDNA library in the yeast Saccharomyces cerevisiae to search for genes conferring Zn tolerance to yeast cells. The screening revealed four A. halleri defensin genes (AhPDFs), which induced Zn but not cadmium (Cd) tolerance in yeast. The expression of AhPDF1.1 under the control of the 35S promoter in A. thaliana made the transgenic plants more tolerant to Zn than wild-type plants, but did not change the tolerance to Cd, copper (Cu), cobalt (Co), iron (Fe) or sodium (Na). Thus, AhPDF1.1 is able to confer Zn tolerance both to yeast and plants. In A. halleri, defensins are constitutively accumulated at a higher level in shoots than in A. thaliana. A. halleri defensin pools are Zn-responsive, both at the mRNA and protein levels. In A. thaliana, some but not all defensin genes are induced by ZnCl2 treatment, and these genes are not induced by NaCl treatment. Defensins, found in a very large number of organisms, are known to be involved in the innate immune system but have never been found to play any role in metal physiology. Our results support the proposition that defensins could be involved in Zn tolerance in A. halleri, and that a role for plant defensins in metal physiology should be considered.

Organization and expression of the GSK3/shaggy kinase gene family in the moss Physcomitrella patens suggest early gene multiplication in land plants and an ancestral response to osmotic stress.

GSK3/Shaggy kinases are involved in a wide range of fundamental processes in animal development and metabolism. In angiosperm plants, these kinases are encoded by moderate-sized gene families, which appear to have a complex set of functions. Here, we present the characterization of five members of the GSK3/Shaggy gene family in the bryophyte Physcomitrella patens. The P. patens GSK3/Shaggy kinases (PpSK) are organized in a group of closely related paralogues with respect to their gene sequence and structure. Indeed, a phylogenetic analysis of the GSK3/Shaggy kinase sequences from plants and animals showed that the five PpSK proteins are monophyletic, and closer to subgroups I and IV described in angiosperms. Expression analyses performed by quantitative real-time RT-PCR on a wide range of growing conditions showed that PpSK genes responded only to either desiccation, PEG or sorbitol. As demonstrated by both inductions of marker genes and protonemal cell plasmolyses, these treatments resulted in a hyperosmotic stress. Altogether, these data suggest that (1) GSK3/Shaggy kinase gene multiplication occurred early in plant evolution, before the separation between bryophytes and vascular plants, and (2) both gene loss and duplication occurred in the ancestor of P. patens along with functional gene diversification in angiosperms. However, conservation of the transcriptional responses between Physcomitrella and Arabidopsis suggests the identification of an ancestral response of the GSK3/Shaggy kinases genes to osmotic stress.

IL-15 availability conditions homeostasis of peripheral natural killer T cells.

Steady-state numbers of peripheral lymphocyte are tightly controlled. For conventional T cells, signals delivered through the interaction of the T cell receptor (TCR) with antigen-loaded MHC molecules are required for the peripheral survival of naive T cells and for their homeostatic expansion in lymphopenic hosts. Cytokines, including IL-7, are also essential for survival of peripheral naive T cells. CD1d-restricted, V alpha 14(+) natural killer (NK)-T cells are a specialized autoreactive T subset with immunoregulatory activity. The relative roles of TCR engagement and cytokine signaling in the peripheral homeostasis of V alpha 14(+) NK-T cells were investigated. After adoptive transfer, the survival and expansion of peripheral V alpha 14(+) NK-T cells was independent of CD1d expression in the host. In contrast, IL-15 (but not IL-7) was required for maintenance of peripheral CD1d-reactive V alpha 14(+) T cells. Comparison of V alpha 14(+) T cell transfers into NK-proficient vs. deficient hosts suggests that NK-T cells and NK cells compete for peripheral resources. Our results indicate that IL-15 maintains the homeostasis of peripheral V alpha 14(+) NK-T cells. In contrast, TCR "tickling" of NK-T cells, if it occurs under steady-state conditions, does not by itself provide a sufficient signal for their peripheral survival.

IL-15 is an essential mediator of peripheral NK-cell homeostasis.

Several distinct classes of surface receptors can, on ligand binding, transmit signals that modulate the survival, proliferation, and apoptosis of peripheral B, T, and natural killer (NK) cells. At the population level, dynamic changes in lymphocyte cell numbers are strictly regulated to maintain a steady state, a process referred to as homeostasis. Although several studies have investigated the signals that regulate B- and T-cell homeostasis, little is known about the mechanisms that control the survival and proliferation of peripheral NK cells. Using an adoptive transfer system, we have investigated the role of gammac-dependent cytokines, in particular interleukin 7 (IL-7) and IL-15, and major histocompatibility complex (MHC) class I molecules in peripheral NK-cell homeostasis. We observed that IL-15 plays a dominant role in the survival of peripheral NK cells, via maintenance of the antiapoptotic factor Bcl-2. IL-15 availability, however, also plays an important role because endogenous NK cells in the recipient mice influence the behavior of adoptively transferred NK cells. Finally, although NK cells bear functional inhibitory Ly49 receptors for MHC class I molecules, the presence or absence of specific ligands on host cells did not influence the survival or homeostatic expansion of donor NK cells.

Combined deficiency in IkappaBalpha and IkappaBepsilon reveals a critical window of NF-kappaB activity in natural killer cell differentiation.

Nuclear factor kappaB (NF-kappaB) transcription factors are key regulators of immune, inflammatory, and acute-phase responses and are also implicated in the control of cell proliferation and apoptosis. While perturbations in NF-kappaB activity impact strongly on B- and T-cell development, little is known about the role for NF-kappaB in natural killer (NK) cell differentiation. Inhibitors of NF-kappaB (IkappaBs) act to restrain NF-kappaB activation. We analyzed the cell-intrinsic effects of deficiencies in 2 IkappaB members (IkappaBalpha and IkappaBepsilon) on NK cell differentiation. Neither IkappaBalpha nor IkappaBepsilon deficiency had major effects on NK cell generation, while their combined absence led to NF-kappaB hyperactivation, resulting in reduced NK cell numbers, incomplete NK cell maturation, and defective interferon gamma (IFN-gamma) production. Complementary analysis of transgenic mice expressing an NF-kappaB-responsive reporter gene showed increased NF-kappaB activity at the stage of NK cell development corresponding to the partial block observed in IkappaBalpha x IkappaBepsilon-deficient mice. These results define a critical window in NK cell development in which NF-kappaB levels may be tightly controlled.

GATA-3 promotes maturation, IFN-gamma production, and liver-specific homing of NK cells.

The GATA-3 transcription factor has a determinant role in T cell specification and is an essential mediator of T helper 2-type polarized immune responses. While both committed NK precursors and mature NK cells express GATA-3, a role of this transcription factor in murine NK cell differentiation is not known. We found that NK cells, in contrast to T cells, can be generated in the absence of GATA-3. However, while GATA-3 antagonizes IFN-gamma production in differentiating T cells, GATA-3-deficient NK cells paradoxically produced less IFN-gamma compared to control NK cells and failed to provide early protection in vivo against infection with Listeria monocytogenes. Surprisingly, GATA-3 was essential for NK cell homing to the liver. Our results suggest that GATA-3 promotes NK cell maturation and acts in this lineage to specify distinct effector phenotypes.